How to combine a blurred emit pass with rest of render?
I would use add here.
When you set the glare nodes to a mix of 1, then they only output the glare, without the original image.

As for the order of the glare nodes, I would apply them all at once.
By applying them one after the other, the next one includes the effect of the previous one in it's calculation, making the result brighter than it should be (and potentially doing things like putting starbursts on the ghost images..).

Instead apply then all to the same source with a mix of 1, then add them together:



Result: